Re: [PATCH v5 0/4] xen/arm: Device Tree based CPU topology support

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Hirokazu,

Please use the add_maintainers.pl script before sending to make sure the right 
maintainers
are in copy of your patches otherwise some might miss your patches.

https://xen.readthedocs.io/en/latest/contribute-xen/submit-patch.html#step-2-use-add-maintainers-pl-or-get-maintainer-pl

Cheers
Bertrand

> On 10 Jul 2026, at 00:05, Hirokazu Takahashi <taka@xxxxxxxxxxxxx> wrote:
> 
> Hello,
> 
> This patch series introduces CPU topology support based on
> Device-Tree and ACPI PPTT for ARM Xen.
> 
> In v5, I added code to parse the ACPI PPTT and reflect it in the CPU
> topology information.
> 
> Future Work:
> - Support for the "credit2_runqueue=cluster" option.
> - CPU topology support for RISC-V and PPC (once SMP support is available).
> 
> Changes in v5:
> - Extracted CPU topology information from the ACPI PPTT.
> - Corrected the erroneous use of CONFIG_CPU_TOPOLOGY to
>   CONFIG_GENERIC_CPU_TOPOLOGY.
> 
> Changes in v4:
> - Only display the CPU topology configuration prompt in common/Kconfig
>   if the architecture defines HAS_GENERIC_CPU_TOPOLOGY.
> - Move the definition of the global 'cpu_topology' pointer to
>   common/cpu-topology.c.
> - Update the Makefile to explicitly build objects as .init.o when all
>   functions and data within a file are annotated with __init/__initdata,
>   ensuring their memory is reclaimed after system initialization.
> - Add an error log in the CPU-to-node mapping function for out-of-bounds
>   cases.
> - Use ARRAY_SIZE() instead of raw macros when guarding array accesses.
> - Rename variables and functions to avoid ambiguous or misleading terms:
>   - Avoid 'cpuid' to prevent confusion with x86 CPUID features/instructions.
>   - Avoid 'node' where it could be confused with a NUMA node, explicitly
>     renaming them to clarify they refer to a Device Tree node.
> - Move local variable declarations into the narrowest possible scope.
> - Replace the unsupported "%pOF" printk format specifier with "%s" and
>   explicit node name retrieval.
> - Remove #include <dt-cpu-topology.h> from cpu-topology.h, and ensure
>   the header directly includes only what its definitions require.
> - Remove #include <xen/device_tree.h> from dt-cpu-topology.h, replacing
>   it with a forward declaration of 'struct dt_device_node'.
> - Use 'const' qualifiers for pointer declarations where the pointed-to
>   structure is not modified.
> - Explicitly #include <asm/processor.h> in cpu-topology.h to guarantee
>   that arch-specific definitions of cpu_to_core() and cpu_to_socket()
>   take precedence over the generic fallbacks.
> - Introduce inline initialization functions for cpu_sibling_mask and
>   cpu_core_mask in cpu-topology.h, providing separate variants for both
>   when CONFIG_GENERIC_CPU_TOPOLOGY is enabled and disabled.
> 
> Changes in v3:
> - Use (nr_cpu_ids - 1) as the maximum CPU ID here. The fix for the sparse
>   map mismatch issue on ARM Xen has been split out into a separate patch.
> - Switch topology sibling masks to cpumask_var_t for dynamic allocation.
> - Allow the system to keep running with a degraded fallback even if
>   the topology table allocation fails.
> - Remove the temporary definitions of cpu_to_core() and cpu_to_socket()
>   from RISC-V and PPC processor.h.
> - Minimize the use of #ifdef blocks, leveraging compiler Dead Code
>   Elimination (DCE) where possible.
> - Clean up the code to follow the Xen coding style. Please let me know
>   if I missed any style nits!
> - Verify successful builds across x86, RISC-V, and PPC environments.
> 
> Changes in v2:
> - Generate topology information even when ACPI is enabled. Note that
>   this is a temporary implementation and doesn't yet parse the PPTT
>   (Processor Properties Topology Table).
> - Added support for cpu-map node in Device Tree that doesn't contain
>   explicit cluster node definitions.
> 
> Changes in v1 from the previous series "Introduce Device Tree based NUMA
> support for ARM Xen":
> 
> 1. Optimized Memory Allocation:
>   The series now allocates only the minimum required memory area to manage
>   the essential data for the CPUs.
> 
> 2. Flexible Device Tree Parsing:
>   The parsing logic no longer depends on the definition order of the 'cpu'
>   nodes and 'cpu-map' nodes in the Device Tree. They can now be read
>   correctly even if their orders do not match.
> 
> 3. CPU Hotplug Readiness:
>   To support future CPU hotplug, the system assumes that inactive CPUs are
>   also described in the Device Tree. Xen will pre-load and generate the
>   topology information for these inactive CPUs during the boot phase so
>   it stays available in memory.
> 
> Thank you,
> Hirokazu Takahashi
> 
> Hirokazu Takahashi (4):
>  xen/device-tree: Parse 'cpu-map' node for CPU topology exploration
>  xen/sched: Link CPU topology to scheduler
>  xen/sched: Make cpu_nr_siblings() architecture-specific
>  arm/acpi: Parse PPTT to initialize CPU topology
> 
> xen/arch/arm/Kconfig                   |   1 +
> xen/arch/arm/acpi/boot.c               |   2 +
> xen/arch/arm/include/asm/acpi.h        |   2 +
> xen/arch/arm/include/asm/processor.h   |   4 -
> xen/arch/arm/smpboot.c                 |  15 +-
> xen/arch/ppc/include/asm/processor.h   |   4 -
> xen/arch/riscv/include/asm/processor.h |   4 -
> xen/arch/x86/include/asm/processor.h   |   1 +
> xen/common/Kconfig                     |  15 +
> xen/common/Makefile                    |   1 +
> xen/common/cpu-topology.c              |  62 ++++
> xen/common/device-tree/Makefile        |   1 +
> xen/common/device-tree/cpu-topology.c  | 406 +++++++++++++++++++++++++
> xen/common/sched/credit2.c             |  21 +-
> xen/common/sysctl.c                    |   1 +
> xen/drivers/acpi/Kconfig               |   3 +
> xen/drivers/acpi/Makefile              |   1 +
> xen/drivers/acpi/topology.c            | 255 ++++++++++++++++
> xen/include/acpi/actbl3.h              |  30 ++
> xen/include/xen/acpi.h                 |  18 ++
> xen/include/xen/cpu-topology.h         |  83 +++++
> xen/include/xen/dt-cpu-topology.h      |  29 ++
> 22 files changed, 923 insertions(+), 36 deletions(-)
> create mode 100644 xen/common/cpu-topology.c
> create mode 100644 xen/common/device-tree/cpu-topology.c
> create mode 100644 xen/drivers/acpi/topology.c
> create mode 100644 xen/include/xen/cpu-topology.h
> create mode 100644 xen/include/xen/dt-cpu-topology.h
> 
> -- 
> 2.43.0
> 
>